‘Diagnosis and treatment’ explains the systems used to classify brain disorders, and the change in our understanding of dementia from seeing it as threshold to a spectrum of symptoms that gradually worsen. There are five main types of dementia: Alzheimer’s, vascular dementia, frontotemporal lobar degeneration, Lewy body disease, and mixed dementia. Neurological disorders also arise from brain trauma, prion disease, substance abuse, Huntington’s disease, Parkinson’s disease, and other conditions. Timely diagnosis is critical to giving patients and their families a sense of agency and, in some cases, the ability to improve symptoms through pharmacological and non-pharmacological means. The most effective treatments are tailored to the individual.